The present invention relates to a method and a device for detecting the impact of a pedestrian with a vehicle, at least one sensor being provided on the bumper and at least one sensor in the area of the front edge of the hood of the engine to measure the pressures or deformations caused by impact and to form a first criterion for the decision as to whether there has been an impact with a pedestrian on the basis of the sensor output signals by comparison with reference quantities.
A method of detecting an impact of a pedestrian with a passenger vehicle is discussed in PCT Publication No. WO 97/18108. To protect the pedestrian from serious injuries in the event of an impact of a pedestrian with the front side of a vehicle, one or more airbags may be provided on the engine hood or on the windshield for deployment in the event of an impact with a pedestrian. Another safety measure for an impact with a pedestrian is for the engine hood to be inclined at an angle to catch the pedestrian. Deployment of such safety devices may depend upon the impact with a pedestrian being detected reliably and also being differentiated unambiguously from impacts with other objects. The related art discusses utilizing for detection of a pedestrian impact the basic kinematics of a pedestrian on impact with the front side of a passenger vehicle. As a rule, the first point of contact of a pedestrian with a vehicle is the bumper. Therefore, a first sensor which responds to the acting force or the deformation may be located on the bumper of the vehicle. Through contact with the bumper, the pedestrian may receive a rotational momentum which throws him onto the engine hood. In other words, impact with the bumper may be followed after a time lag by another impact with the engine hood. Therefore, a second sensor which responds to pressure or deformation may be situated on the front edge of the engine hood. The sensor output signals may be compared with reference quantities that are representative for impacts with a pedestrian. If they match or if there is a correspondence within a certain range of tolerance between the sensor output signals and the reference quantities, it may be decided that this is due to an impact with a pedestrian. As a result of this decision, the available safety devices may therefore be deployed.
An object of the present invention is to provide a method and a device with which it is possible in the event of an impact on the front side of a vehicle to decide with the highest possible reliability whether this impact has been caused by a pedestrian.
An exemplary embodiment of the invention involves at least one sensor mounted on the bumper and at least one sensor in the area of the front edge of the engine hood to measure the pressures or deformations caused by an impact. In the exemplary embodiment, the sensor output signals are compared with reference quantities to derive a first criterion for the decision as to whether it is a pedestrian impact, and the change in velocity and/or acceleration of the vehicle caused by the impact may be determined. By comparing the change in velocity and/or acceleration with a reference quantity, a second criterion for deciding whether it is a pedestrian impact may be formed, and when both decision criteria are met, the decision may be made that it is a pedestrian impact.
In addition to the first known decision criterion, another decision criterion may be formed from the change in velocity and/or acceleration of the vehicle because of an impact, and the decision for a pedestrian impact may be made on the basis of the two decision criteria. Therefore, a high reliability may be achieved in detecting an actual impact with a pedestrian.
In deriving the second decision criterion, it may be expedient to take into account braking which is initiated before an impact, because this has an effect on the change in velocity and/or acceleration of the vehicle caused by an impact. In the case of braking initiated before an impact, the second decision criterion may be derived from the change in acceleration alone because in the case of brake-locked wheels, the velocity sensors present in the vehicle will yield a value of 0. Thus, in this situation, no change in velocity may be determined by comparison of the velocities before and after an impact. The situation may be different with an acceleration measurement, which may be performed independently of movement of the wheels of the vehicle.
Reference quantities for the sensor output signals may include, for example, signal amplitudes typical of a pedestrian impact. The reference quantity used could also be the signal sequence of sensor output signals over time typical of an impact with a pedestrian.
Pressure and deformation sensors based on different measurement principles may also be used. These may include sensors made of wire strain gauges or piezo films or sensors utilizing the anisotropic magnetoresistive effect or the Hall effect. It also may be possible to use sensors having a pressure-dependent light transmission characteristic.